Geog. 309: Urban Environmental Pollution

Lecture 1- The Urban Ecosystem

“Cities are nodes of man’s greatest impact on nature, the places where he has most altered the essential resources of land, air, organisms, and water.”

-Marcus and Detwyler, Urbanization and Environment

The Urban Ecosystem

The city consists of two components: urban man and urban environment

Ecosystem: the organisms of a locality together with their related environment, considered as a unit.

The urban ecosystem is also subject to the principle of environmental unity:all the elements and processes of environment are interrelated and interdependent, and that a change in one will lead to changes in the others.

Three self-evident interactions in an urban ecosystem

• (1) urbanization involves a modification of the environment;

• (2) physical environment may influence the form, functions, and growth of the city; and

• (3) continuous feedback occurs in the city between man, cultural, and physical environments.

• The city is an open system: not self-contained; it cannot operate independently and in isolation from other parts of the world.

• positive and negative feedback:

Positive feedback : is vicious circle or deviation amplification; changes occur in the same direction at a compounding rate.

Example: Population-modernization-migration-population

Negative feedback: equilibrating; dampen fluctuations in the system and maintain a stead state.

Example: Population-air pollution-discomfort and disease-mortality

Urban environment is divided into two classes: 1. cultural (formed by man; it comprises the external

cultural attributes of a given community); and 2. physical subsystem (nature’s elements; exist whether

or not man is one on the scene

The role of environment in the urban ecosystem can be shown by a schematic representation of

feedback loops resulting from interaction of the environmental and cultural subsystem

(a) Population-modernization-migration-population (increase)

(b) Population-air pollution-discomfort and disease-copulation-population (decrease)

The requirements of urban man:

• Biological and cultural requirements: -Air, water, space, energy (food and heat),

shelter, waster disposal

-Political organization,economic system (including labor, capital, materials, and power), technology, transportation and communication, education and information, social and intellectual activities (including recreation, cultural facilities, religion, sense of community), safety.

Fig 1. Inputs and Outputs in an Urban Ecosystem

Resource or Waste Product    (tonnes)

Inputs        

Total tonnes of fuel, oil equivalent 20,000,000

Oxygen       40,000,000

Water       1,002,000,000

Food       2,400,000

Timber       1,200,000

Paper       2,200,000

Plastics       2,100,000

Glass       360,000

Cement       1,940,000

Bricks, blocks, sand and tarmac 6,000,000

Metals (total)     1,200,000

         

Table 1: The Metabolism of Greater London 

Amount per year

Industrial and demolition wastes   11,400,000

Household, civic, and commercial wastes 3,900,000

Wet, digested sewage sludge   7,500,000

CO2       60,000,000

SO2       400,000

NOx       280,000

Table 2. Wastes

Figure 2. Urban Energy Production

Tremendous resource input into a modern city:

• The average urban dweller in the united states uses about 150 gallons of water (directly or indirectly), 4 pounds of food, and 19 pounds of fossil fuels each day

• Each American consumes 1,400 pounds of steel, travels 5,300 miles between cities, receives 400 pieces of mail, and makes 700 telephone calls per year; and in an average day, city’s inputs are converted into 120 gallons of sewage per person, 4 pounds of refuse per capita, and 1.9 pounds of air pollutants per inhabitant (outputs)

Four spheres of physical environment

1. lithologic environment: solid, nonliving portion of the earth; including landforms, bedrock, and soil

2. atmospheric environment: the gaseous envelope of air (and suspended small solid and liquid aerosols) that surrounds the earth

3. hydrologic environment: consisting of the water portion of the earth

4. Biological environment: living things.

http://www.classzone.com/books/earth_science/terc/content/investigations/es0103/es0103page02.cfm

Table 3. Population, Land Area, and Density for the 20 Largest Cities: 1990

Rank CityPopulation(thousands)

Land area(sq. miles)

Density(average

populationper sq. mile)

123456789

10

New York, NYLos Angeles, CAChicago, ILHouston, TXPhiladelphia, PASan Diego, CADetroit, MIDallas, TXPhoenix, AZSan Antonio, TX

7,3233,4852,7841,6311,5861,1111,0281,007

983936

309469227540135324139342420333

23,7007,400

12,3003,000

11,7003,4007,4002,9002,3002,800

11121314151617181920

San Jose, CABaltimore, MDIndianapolis, INSan Francisco, CAJacksonville, FLColumbus, OHMilwaukee, WIMemphis, TNWashington, DCBoston, MA

782736731724635633628610607574

17181

36247

759191

96256

6148

4,6009,1002,000

15,500800

3,3006,5002,4009,900

11,900

Total increase

Major area, region and country 2000 2030 2000-2030

World 2,845,049 4,889,393 2,044,344.0

More developed regions 902,993 1,009,808 106,815.0

(percent) 31.7 20.7 5.2

 Less developed regions 1,942,056 3,879,585 1,937,529.0

(percent) 68.3 79.3 94.8

Least developed countries 167,421 527,162 359,741.0

(percent) 5.9 10.8 17.6

Total World Population 6,055,049 8,111,980

Percent Urban 47.0 60.3

Source: UN 2000. World Urbanization Prospects, 1998 Revisions, Electronic Files

Table 4: Urban Population by Region, 2000-2030